1. Field of the Invention
The present invention generally relates to an internal combustion engine exhaust gas cleaning apparatus and an exhaust gas cleaning method for an internal combustion engine. More specifically, the present invention relates to an exhaust gas cleaning apparatus and method in which a NOx trapping catalytic converter is provided in an exhaust passage.
2. Background Information
Japanese Laid-Open Patent Publication No. 2000-274229 discloses an example of a conventional exhaust gas cleaning apparatus for an internal combustion engine. In the apparatus disclosed in this publication, a navigation system identifies a fueling station where the vehicle was fueled and estimates a sulfur concentration (sulfur content) based on information regarding the identified fueling station. Then, based on the estimated sulfur concentration in the fuel and a fuel injection amount, the apparatus estimates a sulfur poisoning amount of the NOx trap catalytic converter. Based on the estimated sulfur poisoning amount, the apparatus determines if the performance of the catalytic converter has declined and, if necessary, controls a temperature of the catalytic converter and an air-fuel ratio so as to remove the sulfur poisoning from the catalytic converter.